(1) Field of the Invention
The present invention relates to a process for preparing a lower aliphatic hydrocarbon comprising an olefin having 3 or 4 carbon atoms as a main component from a hydrocarbon having 5 to 10 carbon atoms. Furthermore, the present invention relates to a process for preparing a lower hydrocarbon comprising a paraffin having 3 or 4 carbon atoms as a main component by the catalytic cracking by using a specific mordenite catalyst.
(2) Description of the Prior Art
Various investigations have been made from old on the trial to obtain a fraction having 3 or 4 carbon atoms, which is industrially valuable, in a high yield from a petroleum type hydrocarbon compound, represented by naphtha or the like, as the starting material. However, only the thermal cracking is adopted as the industrial process, and the operation is carried out under such conditions that the yield of a fraction having 2 or 3 carbon atoms is highest. As the known process comprising catalytically cracking a hydrocarbon to prepare a paraffin and/or olefin having a reduced carbon number, a process using a silica/alumina type oxide or zeolite as the catalyst is disclosed in "Petroleum Refining Process", page 59 (1978), compiled by the Association of Petroleum and Industrial & Engineering Chemistry, 39, (8), 1032 (1947). However, this process is defective in that a high temperature of 500.degree. to 600.degree. C. or a higher temperature is necessary and hence, the amount formed of a hydrocarbon having 1 or 2 carbon atoms is large and the selectivity to a hydrocarbon having 3 or 4 carbon atoms, intended in the present invention, is low, and that reduction of the activity of the catalyst is violent. In Journal of Catalysis, 6, 278 (1966), it is taught that a hydrogen ion-exchanged mordenite type zeolite exerts an effect for the cracking reaction to a hydrocarbon having 3 to 4 carbon atoms. However, this catalyst is not satisfactory in the selectivity to a hydrocarbon having 3 or 4 carbon atoms and the yield, and the performances are insufficient as the industrial catalyst.
Furthermore, there is proposed a process in which an olefin having 3 or 4 carbon atoms is prepared by dehydrogenating a paraffin having 3 or 4 carbon atoms. For example, there can be mentioned a process in which propylene is prepared by dehydrogenating propane at a temperature of 570.degree. to 680.degree. C. in the presence of a chromium/aluminum type catalyst (U.S. Pat. No. 3,665,049) and a process in which propylene is prepared by dehydrogenating propane at 300.degree. to 700.degree. C. in the presence of a catalyst comprising platinum and magnesium oxide or manganese oxide supported on a zeolite (Japanese Unexamined Patent Publication No. 61-197040). These processes, however, are defective in that the amount formed of a hydrocarbon having 1 or 2 carbon atoms is large and the yield of the intended olefin is low.
In Japanese Unexamined Patent Publication No. 62-22891 proposed by us, there is disclosed a process in which a paraffin and/or olefin having 3 or 4 carbon atoms is prepared by the catalytic cracking of a paraffin having 5 to 10 carbon atoms in the presence of a catalyst formed by treating a metal oxide or composite metal oxide with a fluorine-containing compound. According to this process, the paraffin and olefin are prepared in the form of a mixture, and it is difficult to form the olefin at a high selectivity.